. Oxygen: Preparation: The atmosphere and water contain % and % by mass of oxygen respectively. Most of the world’s rock contain combined oxygen. Industrially oxygen is obtained by fractional distillation of liquefied air.
In the laboratory, oxygen is prepared by one of the following methods. The decomposition of hydrogen peroxide in the presence of catalyst (MnO ) or by oxidation with potassium permanganate. 2H O 2H O + O 5H O + 2MnO + 6H 5O + ⇀ ↽ 8H O + 2Mn + The thermal decomposition of certain metallic oxides or oxoanions gives oxygen. 2HgO 2Hg + O 2BaO 2BaO + O ∆ ∆ 2KClO 2KCl + 3O 2KNO 2KNO + O MnO ∆ ∆ → Properties Under ordinary condition oxygen exists as a diatomic gas.
Oxygen is paramagnetic. Like nitrogen and fluorine, oxygen form strong hydrogen bonds. Oxygen exists in two allotropic forms namely dioxygen (O ) and ozone or trioxygen (O ). Although negligible amounts of ozone occurs at sea level it is formed in the upper atmosphere by the action of ultraviolet light.
In the laboratory ozone is prepared by passing electrical discharge through oxygen. At a potential of , V about % of oxygen is converted into ozone it gives a mixture known as ozonised oxygen. Pure ozone is obtained as a pale blue gas by the fractional distillation of liquefied ozonised oxygen. (O) Oxygen atomic oxygen ⇀ ↽ ⇀ ↽ + ( ) zone The ozone molecule has a bent shape and symmetrical with delocalised bonding between the oxygen atoms.
Figure . Structure of ozone XII XII - - - - Chemical properties: The chemical properties of oxygen and ozone differ vastly. Oxygen combines with many metals and non-metals to form oxides. With some elements such as s-block elements combination of oxygen occurs at room temperature.
Some of less reactive metals react when powdered finely and made to react exothermically with oxygen at room temperature but a lump of metal is unaffected under same condition. These finely divided metals are known as pyrophoric and